WO 96/22802 discloses an inhaler of the above-mentioned type for pulmonary inhalation comprising a tubular body in which an air flow passage is defined. The inhaler comprises only a single dose of an active, inhalable, particulate substance arranged within the air flow passage, said dose being sealed or closed in relation to the ambient atmosphere by closure means which are to be removed or opened by a user prior to use, the inhaler being intended to be used only once. WO 98/53869 discloses a similar tubular body for nasal inhalation.
The closure means of the known inhaler can be caps at each free end of the tubular body, either as two separate caps or as a two integrated twin caps, in case the tubular body is bent to a position with the free ends closely adjacent.
The single dose contained in the inhaler is a particulate material, normally including one or more pharmaceutically active agents, if appropriate, together with conventional pharmaceutically acceptable additives. In the known single dose inhaler, the particulate material often has a volume substantially smaller than the inner volume of the inhaler between the two caps. Because the volume of said particulate material is substantially smaller than the inner volume of the inhaler, said particulate material may be moved and shaken in the inhaler tube during transport and storage, which at least in case of certain preparations, may lead to alterations of particle size, composition of the particulate substances due to segregation, disintegration and crumbling. Further, it is possible that mechanical impact such as shaking will cause the individual grains of the particulate material to stick together or to the inner walls of the tubular body, thus yielding undesired mechanical properties or incorrect dosage. Such alterations may change the inhalation behaviour of the particulate material, jeopardizing the correct administration of the pharmaceutical agent.